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VTA trying to reel in the beast

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#1

12-15-2012, 10:26 AM

nj
pheonix

AK Member

Join Date: Aug 2012

Location: New Jersey

Posts: 2,955

VTA trying to reel in the beast

Hey fellow tubies, I'm in need of
your hard earned experience. In june i built a tubes4hifi vta st120. I'm
using the weber coppertop rectifier. I have the pio coupling caps and the
power supply upgrade caps. I'm using kt120s for the outputs. I've rolled
pretty much everything through the driver board. Somehow i'm missing
something. Amp is loud and clear , imaging is great and i'm not missing
anything high or low, it just seems top is bright. To be fair a lot of
stuff sounds great through it. My best solution has 3 rca long black plate
12bh7s through the driver board. (i have a suspicion that the vta design
to give the modern tube amp design sound forsakes some of the old warmth
of the older tube amp designs, but i'm only guessing). Anybody have any
thoughts, ideas, or suggestions? Thanks for hearing me out

nj pheonix

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#2

12-15-2012, 10:50 AM

Bluelobster

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try changing coupling caps.

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#3

12-15-2012, 11:01 AM

nj
pheonix

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Location: New Jersey

Posts: 2,955

Thanks for the idea. Do you or have
you run across these (this) or is this just a general rule of thumb? also
any suggestions on the replacement. Thanks again for the help.

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#4

12-15-2012, 11:10 AM

battradio

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Location: Near ST. Louis MO

Posts: 4,484

Use tin Foil caps . i built up a ST70
like your and used the diytube driver board http://www.diytube.com/st70/diytube_st70_B.pdf

It sounded its best when it had all tinfoil coupling
caps .The picture still has the one orange drop in it . I built this for
another AKer

Do you have a schematic of the version of the
board you used .

Mark

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I just hate that when you wake up and find out you are
Conti the brain damaged robot and even worse than that the perfect audio
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#5

12-15-2012, 11:16 AM

nj
pheonix

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Location: New Jersey

Posts: 2,955

I should i'll have to check. Its a
low gain (12au or bh7 version). Might have to get back to it i need to
run out . I really appreciate input. I'll dig around and see if i can come
up with schematic. Thanks Again

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#6

12-15-2012, 11:22 AM

nj
pheonix

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Location: New Jersey

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Ok i found schematic lets see if i
can figure out how to upload

Attached Images

driver board schematic.jpg (48.0 KB, 64
views)

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#7

12-15-2012, 12:13 PM

battradio

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Location: Near ST. Louis MO

Posts: 4,484

You have the newest board , it
topolagy is very similar to the diytube by Shannon Parks .Both use the
LM334 constant current scorce , one has used it for over 5 years .

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I just hate that when you wake up and find out you are
Conti the brain damaged robot and even worse than that the perfect audio
system you had is gone !
Mark

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#8

12-15-2012, 02:12 PM

battradio

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Here is the earler board

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I just hate that when you wake up and find out you are
Conti the brain damaged robot and even worse than that the perfect audio
system you had is gone !
Mark

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#9

12-15-2012, 03:42 PM

Dandy

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I see there are some cap upgrade
values on your new schematic for C13 and C15. Out of interest, which did
you use?

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#10

12-15-2012, 08:35 PM

battradio

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Location: Near ST. Louis MO

Posts: 4,484

The cap up grade is for the power
supply and won't affect the problem he has on the top end

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I just hate that when you wake up and find out you are
Conti the brain damaged robot and even worse than that the perfect audio
system you had is gone !
Mark

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#11

12-16-2012, 07:51 AM

rustnrot

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Quote:

Originally Posted by battradio

Use tin Foil caps . i built up a
ST70 like your and used the diytube driver board http://www.diytube.com/st70/diytube_st70_B.pdf

It sounded its best when it had all tinfoil
coupling caps .The picture still has the one orange drop in it . I
built this for another AKer

Do you have a schematic
of the version of the board you used .

Mark

OK, I'll bite, what is a "tin
foil" cap? I have some aluminum foil and wax paper here and ready to roll
but somehow I think I am missing something...

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#12

12-16-2012, 09:20 AM

awise1961

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Location: Nashua, NH.

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On the low gain VTA board I found my
best results were with Janzen Z Superior coupling caps and Sylvania Long
Black Plate 12BH7A's as the outter most tubes and one Raytheon Black Plate
5814 in the center.
My current M125's are running KT120's as well and
I am using Long Grey Plate Sylvania 12BH7A's in the driver board.
I use
the Weber Copper Cap rectifiers when driving my power demanding JBL
250ti's, but I change to NOS Mullard GZ33's for less demanding
speakers.
My M125's are using Russian PIO coupling caps.
If yours
are still new, they take a couple hundred hours to really settle in
nicely.

PS; what preamp and speakers are you teaming this amp up
with?

Al. Wise

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Last edited by awise1961; 12-16-2012 at 09:22 AM. Reason: Added a question

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#13

12-16-2012, 10:25 AM

battradio

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http://angela.com/angelascrtinfoil047uf630vdcsignalcapacitor.aspx

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I just hate that when you wake up and find out you are
Conti the brain damaged robot and even worse than that the perfect audio
system you had is gone !
Mark

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#14

12-16-2012, 11:12 AM

nj
pheonix

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Posts: 2,955

Hi guys, spent the night in philly
last night (wife's xmas party, pretty impressive, anyway i digress. ) OK
Mark, I was a little curious about the tin foil caps. I think Al's link
will be helpfull . I know pio i have now are .22uf. I'm curious how close
the value has to be and the tonal change on raising and lowing the
capacitance. I'm using polk Audio RTI A9s for speakers. I'm using a
tubes4hifi SP13 preamp. (probably not alot of feedback on the pre. its
relatively new (i think i have the first one)). Hey Al, Did you find your
amps running bright until pios broke in? I'd bet i have between 2 and 4
hundred hours on the amp. I think i tried the raytheons in the middle
(with windmill getters). I thought thet were nice but not as nice as
amperex 7316 pqs in the middle. I 'm sure i tried sylvania bh7s or 7a not
necessarily long black plates. I think you both have an inside track on my
issue , Mark apparently very up on the topolgy and Al from experience. So
where am I now? Do i let pios i have now breakin or look for tin foil caps
that match or nearly match values of ones i have.

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#15

12-16-2012, 11:15 AM

nj
pheonix

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Join Date: Aug 2012

Location: New Jersey

Posts: 2,955

P.S. I realize i'm a bit of a nube
with Tube audio and the nuances of sonic effects of tweaking the circuits.
I have some understanding of electronics in general and I'm not quite
follow how the rectifier in the power supply effects the tonal quality of
the output.

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